1. Field of the Invention
The present invention relates to a focus detection apparatus and, more particularly, to a focus detection apparatus which is used in an image pickup apparatus such as an electronic camera or the like and to a control method of such a focus detection apparatus.
2. Description of the Related Art
Japanese Patent Application Laid-Open No. H04-267211 discloses an image pickup apparatus having an image pickup element constructed by two-dimensionally arranging pixels in each of which a photoelectric conversion unit is positioned with being relatively deviated from a microlens. According to the image pickup apparatus disclosed in Japanese Patent Application Laid-Open No. H04-267211, in a normal photographing of an image, an image is formed by adding the pixels in which the relative deviating directions between the microlens and the photoelectric conversion unit differ. In calculation of a focusing position of a photographing lens, the focusing position of the photographing lens is calculated by executing a correlation operation by using a pair of image signals which are generated by pixel series in which the relative deviating directions between the microlens and the photoelectric conversion unit differ.
In such a construction, if a vignetting due to the photographing lens occurs in a light flux for forming the image which is used for calculation of the focusing position, the image signals are nonsymmetric (decrease in coincidence degree of the images) because of the vignetting due to the photographing lens. Therefore, Japanese Patent Application Laid-Open No. H05-127074 discloses such a technique that specific image restoration filters stored in an image pickup apparatus are altered on the basis of an aperture ratio, an exit pupil position, and a defocus amount and applied to image signals, and thereafter, a focusing position is calculated by using the image signals.
According to the related arts, since the image restoration filters are applied to the image signals by a convolution, a pitch of the image restoration filter is made to coincide with a pitch of the image signals.
However, there is such a problem that when the image restoration filters are formed, since a center of gravity of the image restoration filters is deviated, the nonsymmetric images cannot be fully corrected and a focus detection precision is low.